1. Technical Field
The present invention relates to a power supply system or the like provided with a battery (secondary battery) which can be used while repeatedly charging and discharging, and more particularly to a power supply system or the like for determining the life of the battery.
2. Background
Various electrical apparatuses such as, for example, information terminal units represented by notebook-type personal computers (notebook PCs), Mini Disk drives, and video cameras, mainly use a secondary battery as a type of a battery which can be used many times while repeatedly charging and discharging. The secondary battery is typically an inexpensive nickel-hydrogen battery or nickel-cadmium battery having a comparatively large capacity. Sometimes, a lithium-ion battery may be used, which has a high energy density per unit weight compared with a nickel-cadmium battery. Or, a lithium-polymer battery might be used, which uses a solid polymer instead of a liquid electrolyte.
In the case of a secondary battery represented by a nickel-hydrogen battery, nickel-cadmium battery, lithium-ion battery, and lithium-polymer battery, when the life of the battery expires, the operation time of the battery decreases. Therefore, users have a strong desire to know the life of the battery. However, users cannot easily know the life of a battery and therefore, a user may replace a battery with a new one when it is unnecessary to replace the battery.
Currently, one available method of knowing the life of a battery is that of controlling the number of charge and discharge cycles using an intelligent battery containing a microcomputer and determining the life in accordance with the number of cycles. However, the life of the battery fluctuates greatly depending on the operating environment (temperature environment, system load during operation, overcharge state, etc.). Therefore, it is impossible to determine the operating environment of a user by the above method and thus, the method is insufficient for determination of the life of a battery and the battery replacement timing is frequently sub-optimal.
Another method is available for actually charging and discharging a battery and determining the life of the battery in accordance with the capacity of the battery. According to this method, it is possible to almost accurately measure the life of a battery. However, the method requires approximately a half of a full day to know the life of one apparatus because the life of the apparatus is not known until it is charged and completely discharged. Therefore, this method requires an inordiante amount of time and effort. Moreover, in the case of these methods, including control of the number of charge and discharge cycles described above, though an expert can determine the life of a battery by analyzing the battery, it is difficult for a casual user to determine that the battery is near the end of its useful life.
For these reasons, and others readily identified by those skilled in the art, it would be desirable to provide an apparatus and method for determining the remaining useful life of a battery and for communicating such information to a user of the battery.